Open Repair of Descending Thoracic and Thoracoabdominal Aortic Aneurysms

The chest was opened, and a self-retaining retractor was placed for adequate exposure. The aorta was exposed, and the patient was administered 300 units/kg of heparin. Venous cannulation utilized a long dual-stage 25 Fr or 29 Fr cannula, which was passed over a guidewire and directed into the right atrium with TEE guidance. If the venous line cannot be passed safely, typically due to iliac vein stenosis or compression, the left atrium through the left inferior pulmonary vein can be directly cannulated with a 28 or 32 Fr single-stage cannula for venous drainage. If the drainage is not sufficient with a single left atrial cannula (which is frequently the case), the pericardium can be opened over the diaphragm, and the inferior vena cava can be accessed for placement of a right-angled cannula into the right atrium. Alternatively, the main pulmonary artery can be cannulated for venous drainage. The cannula must be placed 1-2 centimeters into the main pulmonary artery to avoid migration into the right or left pulmonary artery. 
 
Cannulation of the femoral artery using the Seldinger technique with a 20 Fr cannula is used in the majority of cases, although stepping down to a 16 or 18 Fr. cannula in smaller vessel diameters may be appropriate in smaller patients. For longer operations (e.g., extent II or III thoracoabdominal aortic aneurysm repairs), a 6 Fr. distal perfusion cannula is placed in the antegrade direction into the common femoral artery to perfuse the cannulated limb and avoid ischemia. Occasionally, the common femoral artery is very small, requiring suturing of an 8 mm Dacron graft to the femoral artery. 
 
If there is significant iliac and femoral peripheral arterial disease or severe mobile atheromatous disease, cannulation of the descending thoracic aorta or distal aortic arch is preferable. 
 
Cardiopulmonary bypass was gradually instituted, allowing the heart to continue ejecting blood into the arch vessels initially. Arterial blood was cooled to 15 degrees Celsius, and the cooling period lasted a minimum of 30 minutes. 
 
During cooling, the pericardium was opened over the left ventricular apex immediately after the heart fibrillated, and a 14 Fr left ventricular decompression catheter was inserted through a stab incision in the left ventricular apex. Adequate left ventricular decompression is especially important if any aortic insufficiency exists to avoid pulmonary venous congestion in the lungs. Pulmonary venous congestion, along with left lung manipulation while systemically anticoagulated, could cause troublesome intraparenchymal bleeding from the left lung. Avoiding pulmonary artery pressures greater than 15mmHg through left ventricular decompression and using very gentle traction on and manipulation of the left lung are critical in minimizing this complication. 
 
The proximal extent of the aneurysm was exposed. Dissecting proximal to the aneurysm to the left common carotid was not necessary since aortic clamps are rarely used. Typically, the vagus nerve and the left recurrent laryngeal nerve are identified and minimally manipulated to gain access to the proximal anastomotic site. Intercostal arteries of the proximal half of the descending thoracic aorta were ligated and divided on the outside of the aorta, minimizing manipulation of the aneurysm. Significant manipulation of the aneurysm may cause dislodgment of thrombus or atherosclerotic debris, which would likely embolize proximally during retrograde aortic flow. Ligating the high intercostal arteries on the outside of the aorta prior to opening the aneurysm may prevent a steal phenomenon of spinal cord blood flow (8, 9). Intercostal arteries in the distal half of the descending thoracic aorta were not ligated, not only to allow cold blood perfusion of the distal cord but also to save them for reimplantation later in the procedure. A small polyethylene tube was passed around the mid descending thoracic aorta, staying close to the aortic wall to avoid damaging the large lymphatic vessels and the hemiazygos vein. This tube marked the site for placement of the cross-clamp during formation of the proximal anastomosis. Encircling the aneurysm should be performed at a place where the aneurysm narrows, if possible. 
 
Once hypothermia had been achieved (a minimum of 30 minutes of cooling, and up to 45 minutes of cooling when a complex proximal anastomosis is anticipated), the patient was placed in a steep Trendelenburg position and rotated to the patient’s right to place the ascending aorta in the most dependent position. Positioning in this manner helped keep air out of the aortic arch branches. Cardiopulmonary bypass was stopped, and the LV suction was halted. If suction on the LV decompression had been continued, it would have entrained air into the transverse arch, ascending aorta, and left ventricle. The venous line was clamped immediately to avoid exsanguination into the cardiopulmonary bypass reservoir, and only after cessation of arterial flow was an aortic clamp placed across the aorta where it had been previously encircled with the polyethylene tube. 
 
Next, the aneurysm was opened proximally from the cross-clamp to the intended proximal anastomotic site. Once the aneurysm was cleared of blood, taking care not to suction blood below the openings of the innominate and left carotid arteries, the surgeons directly inspected the proximal lumen for atheromatous debris or clot. After the brief inspection and finding no need for further proximal exposure, the femoral arterial flow was resumed at 1 to 1.5 L/min, keeping the venous line partially occluded or nearly occluded. A flexible suction catheter was placed in the open proximal aorta, avoiding exposure of the orifices of the innominate or left common carotid arteries to air. If too much blood prevents visualization of the anastomosis during proximal suturing, then the venous line can be opened slightly to allow drainage of the heart. It is important to find an area in the distal or transverse arch devoid of debris for the proximal anastomosis, which, at times, requires resection of nonaneurysmal aorta. The surgeons avoid the urge to debride intraluminal plaque in the aorta proximal to the anastomosis because these attempts can result in cerebral embolization. 
 
A 26-30 mm Dacron graft with a 10 mm perfusion sidearm was sewn to the open proximal aorta using 3-0 polypropylene suture. The sidearm was kept within 2-3 cm of the proximal anastomosis. Proximal flow was established via a second arterial line with a separate rollerhead at 1 L/min through the perfusion sidearm. If the CTA indicated severe atherosclerotic disease of the transverse aortic arch, then left or right common carotid or right axillary artery cannulation may be used for proximal arterial inflow rather than the perfusion sidearm to avoid retrograde flow in the arch. After proximal anastomotic hemostasis was inspected and secured, proximal arterial flow was temporarily discontinued, and blood was aspirated from the graft proximal to the anastomosis. The anastomosis was then dried on the outside and sealed with a biological adhesive. Taking a few minutes to seal the anastomosis properly was invaluable in minimizing needle hole bleeding, especially when multiple anastomoses were anticipated. A cross-clamp was placed immediately distal to the perfusion sidearm, and proximal arterial flow was resumed at 1 L/min or more to maintain a right radial arterial pressure of 40 mmHg or higher. Left ventricular decompression was resumed only at this time. Any back bleeding from intercostal arteries proximal to the cross-clamp was ligated. Ligating these intercostal arteries at this point minimized steal from the spinal cord for the remainder of the operation. 
 
The patient was then placed in reverse Trendelenburg position, and the femoral arterial flow was stopped while continuing proximal flow with the venous line partially occluded. The cross-clamp at the mid descending thoracic aorta was removed, and the remainder of the aneurysm was opened. Patent intercostal arteries in the lower descending thoracic aorta were identified and incorporated into the distal anastomosis, leaving them in situ on the native remaining aorta. If such an anastomosis can complete the repair, the arterial blood is warmed to 37 degrees Celsius during the suturing of this distal anastomosis. 
 
During the warming phase, after 10 minutes of proximal blood flow at 30 degrees Celsius or higher, the first attempts were made to defibrillate the heart. Lidocaine (100 mg) and magnesium sulfate (1 g) were administered directly into the cardiopulmonary bypass circuit to help maintain sinus rhythm once the heart had been defibrillated. Once the ventricles began to contract, the right lung was ventilated. At this stage, with venous flow restricted and the right heart partially filled, right lung ventilation may prevent the heart from ejecting deoxygenated blood into the aortic root and into the coronary arteries, which could have produced North-South syndrome. 
 
Once the distal anastomosis was completed and sealed with a biological adhesive, the graft was carefully de-aired. The patient was switched to the Trendelenburg position during de-airing, as air can be trapped in the graft. The cross-clamp distal to the side arm was removed. Flow was increased to the patient's calculated blood flow, and venous line drainage was unrestricted. Meticulous surgical hemostasis was obtained and is greatly simplified if there is proper sealing of the anastomoses and needle holes. The femoral arterial cannula was removed during warming, with flow solely through the sidearm graft, allowing unimpeded perfusion of the left leg. 
 
Once normothermia and hemostasis were achieved, the left ventricular decompression was removed. The site was repaired while on cardiopulmonary bypass. This repair can be challenging, especially if significant aortic insufficiency exists. In this case, dropping cardiopulmonary bypass flow to 1 L/min with the venous line unrestricted to empty the heart facilitated the repair. 
 
Weaning from cardiopulmonary bypass frequently requires inotropic support (norepinephrine or epinephrine) in the first few hours to maintain a mean arterial pressure of 70-90 mmHg. Transesophageal echocardiography was useful in assessing ventricular function and volume status. The venous line was removed, and the femoral vein was repaired, taking care not to narrow the cannulation site. The motor-evoked and somatosensory-evoked potentials were monitored every 15-30 minutes after separation from cardiopulmonary bypass. If the motor-evoked potentials are not present in the lower extremities, the mean arterial pressure is elevated to 90-110 mmHg and a lumbar drain is placed immediately after closure. If a drain is already present, cerebrospinal fluid is aggressively drained to a target cerebrospinal fluid pressure of 10 cm H20. 
 
Thoracoabdominal Aneurysm Repair 
 
The thoracoabdominal aneurysms were repaired using the same technique as for descending thoracic aneurysm repair proximally. After the proximal anastomosis was completed and higher intercostal arteries were ligated, the repair proceeded. 
 
The clamp on the mid descending thoracic aorta was relocated to the supraceliac aorta. The descending thoracic aorta was opened to expose the intercostal arteries of the distal descending aorta. Perfusion proximally via the graft side arm and distally via the femoral arterial cannula was continued. 
 
To minimize the ischemic insult to the spinal cord and abdominal viscera, the perfusion circuit remained cold. Attempts were made to keep adequate cold perfusion to as many as three sources of blood to the spinal cord (via the vertebral arteries, segmental intercostal and lumbar arteries, or internal iliac arteries). Maintaining a mean arterial pressure of 50-60 mmHg with increased proximal arterial flow can achieve adequate spinal cord perfusion when the other sources of spinal cord oxygen delivery are temporarily stopped. Patent intercostal arteries in the region of T8-L1 were revascularized as an island using either direct implantation to the thoracoabdominal graft or a 10 mm looped Dacron graft. Only after resuming segmental arterial blood flow to the lower spinal cord was the patient’s arterial blood warmed to 20 degrees Celsius.  
 
The femoral arterial flow was stopped, the supraceliac aortic cross-clamp was removed, and the remainder of the aneurysm was opened to the aortic bifurcation if necessary. If the clamp can be placed in the infrarenal aorta, arterial flow can be resumed through the femoral artery to perfuse the lower extremities and pelvis. Care was taken not to injure the left renal artery, which lies 1-2 cm caudal to the median arcuate ligament. 
 
The four visceral branches were perfused at low flow (200-350 mL/min) with 10–18-degree Celsius blood via 9 Fr balloon perfusion catheters. These perfusion catheters were placed immediately after opening the lower portion of the aneurysm and prior to removal of thrombus from the aneurysm sac. Visceral arteries were reattached by separate grafts (a Coselli graft could be useful, especially in patients with multiple ostial stenosis or connective tissue disorder) or as an island or button. An island anastomosis can be chosen if there is not a significant amount of distance between the visceral artery orifices to avoid incorporation of aneurysmal aortic tissue in the repair. 
 
Occasionally, an island of celiac, superior mesenteric, and right renal arteries are sutured to a separate 14 mm Dacron graft, which, in turn, is connected to the main thoracoabdominal graft proximally. Flow was reestablished to these visceral arteries, and the proximal clamp was moved below. At this point, cardiopulmonary bypass flow was increased to 2.5 to 3 L/min, and the patient was warmed to 30 degrees Celsius. At 30 degrees Celsius, if multiple lower intercostals had not been reimplanted due to chronic occlusion, the radial arterial mean pressure is maintained at 80 mmHg or higher, since vertebral arteries may be the primary source of spinal cord blood flow. 
 
The inferior mesenteric artery, if greater than 2-3 mm in diameter and/or associated with chronic occlusion of the celiac or superior mesenteric artery, should be considered for reimplantation. If an inferior mesenteric artery is ligated and diarrheal stool occurs in the first six hours postoperatively, one should consider emergent return to the operating room and revascularize the inferior mesenteric artery if possible. Major morbidity and mortality have occurred from routine ligation of this seemingly unimportant artery. 
 
The distal anastomosis was then completed at the aortic bifurcation, and the thoracoabdominal graft was meticulously de-aired. In the setting of iliac artery pathology, an aorto-bi-iliac graft is often required for appropriate distal reconstruction. The patient was fully rewarmed, the left ventricular decompression catheter was removed as outlined above, and the patient was separated from cardiopulmonary bypass. Protamine was administered, and surgical hemostasis was obtained. 
 
An intercostal nerve block was performed on all patients to provide immediate analgesia (0.25 percent bupivacaine hydrochloride and epinephrine bitartrate). The diaphragm was closed with a running #1 polypropylene suture. The abdominal wall musculature was closed in one layer with #1 polydiaxanone suture. Large braided #5 Ethibond paracostal sutures were placed to reapproximate the ribs. Ribs that were divided at the beginning of the procedure were reapproximated with 12- or 16-hole titanium plates. The cut ends of the costochondral margin should meet as the ribs are reapproximated and should not overlap to avoid chronic nonunion of the costal margin. 

References

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